Electrical insulation containing a molecular sieve having adsorbed perhalogenated fluid



Feb. 21, 1967 J. c. DEvzNS 3,305,656

ELECTRICAL INSULATION CONTANING A MOLECULAR SIEVE HAVING ADSORBEDPERHALGENATED FLUID Filed Dec. 26, 196s H/'s Agenf.

United States Patent O 3,305,656 ELECTRICAL INSULATION CONTAINING A M-LECULAR SIEVE HAVING ADSORBED PERHAI.- OGENATED FLUID John C. Devins,Burnt Hills, N.Y., assgnor to General Electric Company, a corporation ofNew York Filed Dec. 26, 1963, Ser. No. 333,373 13 Claims. (Cl. 200-144)The present invention relates to improvements in insulation forelectrical apparatus and, more particularly, to improved organicinsulation which protects electrical devices subject to electricaldischarge conditions and to methods for making such insulation.

Certain types .of electrical equipment frequently experience electricaldischarges between points of different potentials. Illustrative of thecauses of such discharges are the conditions of over-voltage, opening ofthe circuit, for example as by a switch, blowing of a fuse due tooverload on the circuit, etc. Such electrical discharges cause arcs toform which permit the current to continue to iiow in the opened circuit.It is highly desirable to distinguish such arcs as rapidly as possible,to stop the liow of the current.

Other types of electrical equipment are subject to corona discharge int'he insulation separating an electrical conductor from a source ofhigher or lower electrical potential. This corona discharge causesdeterioration of the insulation so that rIinally failure .of theelectrical apparatus occurs, unless the load on the equipment is reducedbelow those conditions causing corona discharge. This means that thecapacity of the electrical apparatus to perform its function isseriously reduced. Corona discharge starts in the voids formed eitherduring the fabrication of the insulation or later due to stresses andstrains developed during fabrication or during operation. Therefore, itis highly desirable to increase the dielectric strength of such voids sothat corona discharge will not occur in normal operation of theequipment at its rated capacity.

Organic resinous materials, including both the natural and syntheticresinous material, generally have good electrical insulating properties.However, the methods of which they are fabricated into the desiredshape, for example, by compression, injection, and extrusion molding,laminating, melt or solution coating, etc., have the inherentdisadvantage that they tend to create voids in the fabricated part whichseriously affect their insulating properties. It would be desirable toincrease the dielectric strength of such voids so as to increase theinsulating properties of these materials. Furthermore, some of theseorganic resinous materials have good arc extinguishing properties due totheir ability to evolve a gas when an electrical arc is directed overtheir surface. However, it would be desirable to increase the arcextinguishing properties of these materials by increasing the amount ofgas which is given olf by a given weight of such materials under theheat of the arc, as well as supplying a gas which has better arcextinguishing properties.

Accordingly, it is one object of this invention to provide electricalapparatus having organic insulating components which have increasedability to extinguish arcs occurring in such electrical apparatus.

It is another object of the invention to provide an improved electricalapparatus having .organic insulating components having improved coronastarting voltage characteristics.

It is another object to provide a method of preparing such improvedelectrical insulation.

These Iand other objectives are .obtained in accordance with the presentinvention by incorporating in such synthetic resinous materials aperhalogenated fluid having a dielectric strength greater than airadsorbed on a molecular sieve dispersed in the organic resinousmaterial. The scope of the invention ralso includes the methods wherebythese compositions are made.

Although the features of this invention which are novel are set forth inthe appended claims, greater detail of the invention in its preferredembodiments and the further objects and advantages thereof may bereadily comprehended through reference to the following description,taken in connection with the accompanying drawings, wherein:

FIG. 1 is a cross-section of an insulated electrical conductor embodyingmy invention;

FIG. 2 is an isometric View partly broken away, showing a portion ofdisconnect switch having an associated arc suppressing shield embodyingmy invention;

FIG. 3 is an elevational view partly in section of an electric circuitbreaker of the expulsion type having an arc suppressing shield embodyingmy invention;

FIG. 4 is an isometric view showing a schematic view of a switch havingan arc chute embodying my invention;

FIG. 5 is a sectional view of an expulsion fuse unit consisting of afuse holder of conventional design and a removable fuse link having anarc suppressing shield embodying my invention;

FIG. 6 is an enlarged sectional view of the fuse link shown in FIG. 5;

FIG. 7 is a perspective view of a molded-casing type transformerembodying my invention; and

FIG. 8 is a cross-sectional view of the transformer along line 88 ofFIG. 7.

In FIG. l there is shown by way of example a solid conductor 1surrounded by an insulation 2. The conductor 1 may be either of a solid,tubular or multiple-strand type of electrical conductor such as copper,silver, aluminum, etc. As is conventinonal in the art, conductor 1 maybe electro-plated with another metal, e.g., nickel, if desired.Insulation 2 may be either tightly bound to the conductor as when theinsulation 2 is extruded or wound onto the electrical conductor 1, or itmay be of the sleeve type which is slipped over the conductor 1 in aloose fitting relationship. Insulation 2 comprises a composition of thisinvention hereinafter described in further detail.

.FIG. 2 illustrates one set of contacts of a disconnect switchcomprising a fixed contact in the form of a pair of opposed spring jaws10V and a movable contact in the form of a blade 11 insertable betweenthe jaws 10 when the switch is closed. Each of the jaws 10 convenientlyforms one leg of an L-shaped strip of metal, the other leg 12 of whichis secured to a switch base 13 as by a bolt 14. The arc suppressingcomposition forms a simple shield cornprising a pair of L-shapcd partseach having a short leg 15 and a long leg 16. The longer legs of the twoparts are held in engagement with each other as by Abolts 17 and havetheir opposed faces recessed to receive the contact jaws 1li and theswitch blade 11 and to provide a chamber 18 into which the contact jaws10 and switch plate 11 extend. The shorter legs 15 are recessed to clearthe legs 12 of the stationary contacts and the heads of the bolts 14 andare secured to switch base 13 by bolts or screws 19. The arc which formsupon separation of the mova-ble and stationary contacts is enclosed in achamber the walls of which are molded of the composition hereinafterdescribed.

There is shown merely by way of example in FIG. 3 a circuit breakerhaving means such as the stationary contact 30 and the movable rodcontact 31 for opening the circuit causing an arc to form and aninsulating structure 32 forming an arc chamber for closely conning thearc 'between the contacts. The insulating structure 32 comprises atubular member closed at the one end by contact 3 30 and open at theother end for receiving the rod contact 31. On opening of the circuit,separation of the contacts 310 and 31 causes formation of an arc theheat of which releases some of the gas adsorbed on the filler in thematerial of the arc chamber walls, the composition of which ishereinafter described in more detail. The air already in the arc chamberand the gas emitted from the chamber walls 32 is under considerablepressure when released by the arc formed between contacts 3u` and 31,due to the close fit of the rod contact 31 in the tube 32, with theresult that when the rod leaves the tube a blast of gas is released asindicated, causing the arc to be interrupted.

FIG. 4 shows an alternative construction of a switch andarc-interrupting device wherein the two contacts 41 and 42 are movedrelative to each other to make and break electrical contact. Onseparation of electrodes 41 and 42 an arm forms which is magneticallydeflected yby a conventional blow-out coil (not shown) so that the arcplays into the space between the arc chute plates 40 formed of thecomposition hereinafter described in detail, which lare held together inspaced relationship by spacers 43 acting in cooperation with bolts 44and nuts 45. The heat of the arc playing on the surface of plates 40causes a gas adsorbed in the composition to be released, extinguishingthe arc.

' FIG. 5 is an illustration of a fuse holder having within a main tubeportion an inner or auxiliary expulsion tube surrounding a removablefuse link. The casing or fuse holder of the expulsion fuse unit consistsof a fuse tube 50 comprising or having an insulating base materialsurfaced with the composition of this invention, hereinafter describedin more detal. The contacts 51 and 52 are mounted at either end of thefuse tube 50 for connecting the fuse unit in the circuit by mounting ina suitable fuse support or otherwise. The cap 57 which closes one end ofthe tube 50 isscrewed onto the contact 52, providing a clampedelectrical contact with the button-head 58 of the fuse link 55. Othersuitable clamping means 53 and 54 are provided for similarly clampingthe lower terminal 59 of the fuse link 55 to the contact 51. Theexplosion chamber of the fuse holder consists of the central bore of thefuse tube S and the chamber formed by the contact 52 and its extension56. The walls of the fuse tube 50 are of suicient thickness to withstandthe gas pressure generated when the fuse is blown.

As shown in FIG. 6, the fuse link 55 of FIG. 5 comprises a fusibleelement 60 enclosed in a thin-walled tube 61 comprising a highlyinsulating base material described hereinafter. The fusible element`6tl'rnay be of tin or other fusible metals or alloys, either in wire orstrip form, so shaped that blowing occurs near the upper end of the tube61. The tube 61 is closed at ond end by a stopper 62 which is cementedin position to seal the end of the tube. The stopper 63 is placed in thebottom of the tube `61 with a snug fit to permit gas pressure to buildup within the tube when the fuse link is blown by light current.However, this stopper is not indispensable and may be omitted. Thefusible link 60 is connected by means of a hard metal wire 64 whichpasses through stopper 62 to the button 58. The other end of the fusibleelement 60 is connected to the terminal wire 59 which passes through thestopper 63. The chamber formed by the @bore of tube 61 is small enoughto produce the necessary gas pressure to extinguish the arc when thefuse blows on light currents. When a heavy current fault occurs, theextremely high gas pressure generated in `a manner such as hereinafterdescribed, bursts this tube and permits the gas to expand within thelarger explosion chamber, thus reducmg the gas pressure to a safe valueand furnishing the normal arc extinguishing action of the largerchamber. 'I 'hus, the combination of the small tube 61 of the fuse lmk55 with the larger tube 50, produces an expulsion fuse which hasimproved operating characteristics on small currents and yet operateswith equally satisfactory characteristics on high short-circuit curljlllWill-e:

FIGS. 7 and 8 show a current transformer having primary terminals 70 and71 and secondary terminals 72 and '73. The positioning of the primarywindings 8@ and the secondary windings 81 will be apparent from the viewof FIG. 8. These windings are electromagnetically linked with a core 82of magnetic material which is provided with a pair of tubular separators83 and 84, which serve t-o insulate the core from the windings. Thetransformer includes a molded or cast component 74 which encapsulatesthe various components, as shown, and thereby provides a completephysical enclosure as well as electrical insulation. A support platefacilitates mounting.

FIGS. 1, 7 and 8 are typical of the electrical devices in which amassive amount of insulation is in contact with an electrical conductorso that, in use, when a current is flowing in the conductor, electricaldischarge between the conductor and a potential of higher or lower valueis prevented by the insulating characteristics of the insulation. Duringsuch use, the insulation is subject to voltage stress, which if greatenough, causes corona discharge to occur in any voids which may bepresent in the insulation. As mentioned previously, the means ofproviding the insulation for such electrical apparatus has the inherentdisadvantage that it is practically impossible to producesuch a solidmass of insulation without incorporating the voids due either to theentrapment of air or to the creation of voids due to physical stressescreated during the formation of the insulating member, or caused byoperating conditions.

For example, one method of making the insulated electrical conductorshown in FIG. l is that wherein the conductor 1 is passed through anextrusion machine and insulation 2 is extruded onto the electricalconductor. Since the insulation is fed to the extrusion machine in theform of comminuted material, air is occasionally entrapped in theinsulation in the form of extremely minute bubbles which escape visualinspection and therefore form weak spots inthe insulation. In anothermeth-od of making such insulated conductor, the insulated electricalconductor as a solid rod or tube is used as a mandrel and the insulationis wound onto the conductor in the form of a fibrous web such as clothor paper, which has either been previously impregnated with a solutionof the organic resinous material acting as the insulation, or thefibrous web is passed over a heated apron and the organic resinousmaterial melted onto the heated web to impregnate it as it is wound ontothe conductor. Entrapment of air can occur in such a process, or voidsare created during the curing process.V If the organicresinous materialis a thermosetting resin, the strains caused during the curing processcause voids to form between the convolute wrappings of the web aroundthe conductor. Sleeve-type insulation is also made by either extruding atubing of the insulation or by stripping the tube from the mandrel onwhich the insulation is wound in the form of a laminated tube.

Ign making electrical apparatus such as encapsulated apparatus, asillust-rated by the encapsulated current transformer of FIGS. 7 and 8, asynthetic resinous material is used to encase the apparatus either in amolding operation whereby the uidized Vresinous material is caused to owunder pressure around the components of the apparatus, for example, thewindings and core of the transformer, or the organic resinous materialin the form of a liquid is used to impregnate and encase the componentparts using a mold as a container to give the desired shape. In eitherof these two methods, it is practically impossible to insure that theresinous material completely displaces all of the void space, especiallyaround wires or other components such as metal strips which are closelyspaced together, even though the molding is carried out under highpressures, or the impregnation with a liquid is carried out undervacuum.V Furthermore, during the curing operation, gases or vapors ofthe insulating material are sometimes given olf =due to the vaporpressure of the components of the resinous material itself whichlikewise cause voids to form in the resin. Furthermore, When suchapparatus is operated, heat is generated within the metallic componentsof the electrical apparatus which causes differential expansion betweenthe metal parts and the organic resinous material which causes voidswhen the apparatus cools.

Since the air, gases -or even the vacuum created by such voids has alower dielectric strength than the insulation itself, such voids form aweak spot in the insulation which can cause prematu-re failure of theequipment or at best require the equipment to be operated at a lowerrating than would be possible if the insulation were free of such voids,or if the voids had increased dielectric strength.

In the making of electrical devices where arc extinguishingcharacteristics are desired, for example, as illustrated by theapparatus in FIGS. 2, 3, 4, 5, and 6, although certain organic resinousmaterials are capable of producing a gas when subjected to an arc, thegas is produced by actually thermally decomposing the organic resinousmaterial and the amount of gas available `for the a-rc extinguishingfunction is limited by the amount of material thermally decomposed bythe arc. Since the arc interrupting capacity of these devices could beincreased if either or both the amount of gas released and the arcextinguishing ability of the gas were increased, it is highly desirableto increase either or both the gas producing ability of the organicresinous materials and the ability of the evolved gas to extinguish anelectric arc.

I have now found that both of these problems facing electrical equipmentmanufacturers can be readily overcome by incorporating in the syntheticresinous material a molecular sieve having adsorbed thereon aperhalogenated fluid having a dielectric strength greater than air. Suchmaterials can be used as molding compounds to either make molded partsor used in the form of fluids to make cast or impregnated parts. Now,even if voids are formed in the insulation, the adsorbed perhalogenatedfluid desorbs from the molecular sieve and diffuses into the void space,increasing the dielectric strength. Under the heat of an electric arc,the adsorbed perhalogenated uid is also desorbed from the molecularsieve and forms a gas which greatly increases the amount of gasavailable to extinguish the arc. At the same time, the high dielectricstrength of the gas from the perhalogenated fluid enables it to morerapidly extinguish the arc than the gas given off by the decompositionof the organic resinous material.

The types of organic resinous materials may be either naturallyoccurring gums, for example, rosin, shellac, kauri, copal, tars, i.e.,from coal tar distillation, distillation of tree pitches, etc., naturalrubber, etc.; synthetic Cil organic resinous materials., lboththermoplastic and therr mosetting, for example, phenolic resins, urearesins, melamine resins, polyethylene, polypropylene, polybutene,polytetrafluoroethylene, polytriuoroethylene, polyvinyl chloride,polyvinylidene chloride, chlorinated polyethylene, chlorosulfonatedpolyethylene, polymethylmethacrylate, etc., including the variouspolymers, copolymers and mixed polymers of these materials, for example,blends and copolymers of polyethylene and polypropylene, blends ofphenolic resin with synthetic rubber; synthetic rubbery polymers, eg.,polybutadiene, polyisoprene, polychloroprene, etc., including thevarious copolymers and mixed polymers of these materials, for example,butadiene-acrylonitrile copolymers, butadiene-styrene copolymers,isoprene-butadiene copolymers, butadiene-butene-l copolymers, etc.;epoxy resins, polyester resins, including the solventless varnish typeof polyester resins, wherein a polymerizable monomer for example styreneis used as the solvent for an unsaturated polycarboxyl'ic acid ester ofa polyhydric alcohol, polycarbonate resin, etc. The choice of theparticular organic resinous material for a particular application isbased solely upon its physical and chemical properties.

'Ihe molecular sieves useful for my invention as well known,commercially available materials both of the natural and synthetic type.They are crystalline zeolites having good sorption characteristics forvarious uids because of the myriad of pores or capillaries present intheir crystal structure. They are available in Various grades determinedby the pore size. Depending on the pore size, these materials vary incapacity to adsorb various fluids, i.e., liquids and gases. The abilityof these various materials to adsorb a wide variety of fluids has beenthe subject of many investigations and is well documented in theliterature, for example, in the book, Molecular Sieves, by Charles K.Hersh, Reinhold Publishing Corporation, New York, New York (1961), andthe literature references cited therein. Because of their ability toadsorb various fluids, they have found extensive use as drying agents,as carriers for various chemical reagents, for example, curing agents inthe compounding of moldable compositions, as the carrier of foamingagents in the compounding of foamable, molda'ble cornpositions, etc. Inthese applications, the adsorbed material is released during the moldingoperation to perform the function of either curing or foaming the moldedmaterial during the molding operation.

The ability of a particular molecular sieve to adsorb a particularmolecule is related to the pore size of the molecular sieve and thecritical dimension (width, depth or diameter; length is not critical) ofthe material to be adsorbed. If the critical dimension of the moleculeto be adsorbed is greater than the pore size of the molecular sieve,little or no adsorption takes place. However, if the reverse is true,then the molecular sieve can readily adsorb the other material. When thepore size of the molecular sieve is considerably greater than thecritical size of the molecule of the material to be adsorbed, then thematerial is very easily adsorbed and the actual quantity adsorbed isgreater than for a molecular sieve whose pore size is only slightlygreater than the dimensions of the molecule to be adsorbed. Conversely,however, the ease with which the absorbed material is desorbed under theinfluence of either heat or reduced pressure increases when the poresize of the molecular sieve is increased in relation to the criticalsize of the molecule of the adsorbed material. Increasing the vaporpressure of the fluid and decreasing the temperature at which theadsorption is performed increases the amount of adsorption of a givenfluid on a particular molecular sieve, and vice versa. The influence oftemperature, which governs the quantity of uid adsorbed or desorbed,appears to be greater than the influence of vapor pressure of the fluidwhich governs the rate of adsorption and desorption.

In the specification and claims, I use the term perhalogenated fluid todescribe the various liquids and gases having the maximum amount ofhalogen associated with the compound, i.e., a perhalogenated alkane hasall the possible 'hydrogens replaced with a halogen. Because of theirready availability and excellent dielectric strength, I prefer to use asthe perhalogenated fluid one or more of the following: sulfurhexafluo-ride, selenium hexafluoride, and the fluid perhalogenatedalkanes. Of the various perhalogenated alkanes, I prefer those havingfrom 1 to 8 carbon atoms and especially those in which the halogen istluorine or chlorine. Of these, only carbon tetrafluoride does not havea dielectric strength greater than air. Typical of the variousperhalogenated alkanes which I may use are, by way of example, carbontetrachloride, trichlorofluoromethane, dichlorodifluoromethane,chlorotriuoromethane, bromotrifluoromethane, trichlorotriuoroethane,diohlorotetratluoroethane, dibromotetrauoroethane,chloropentalluioroethane, hexalluoroethane, hexatluoroethane,octauoropentane, decafluorobutane, octafluorocyclobutane,dodecylluoropentane, tet-radecyltluorohexane, octadecyliiuorooctane,pentauorothiotrifluoromethane (CF3SF5), etc. These compounds are eithergas or liquid and have a boiling point no greater than 90 C. andtherefore have sufficient vapor pressure that they will supply a gaseousatmosphere at the temperature at which they are used in my applications.In addition, they are excellent dielectric fluids.

The choice of the particular perhalogenated fluid and the particularmolecular sieve is based on the application of the combination of thetwo as a filler in the organic resinous material, and theV method bywhich the particular component of the electrical apparatus is to befabricated. For example, if the composition is to -be used Ifor makinginsulation, for example, an insulated electrical conductor, or theencapsulation of the piece of electrical apparatus, yfor example, atransformer where the purpose of the adsorbed perhalogenated fluid is tooccupy any voids created in the apparatus either during fabrication oruse, then one ldesires to choose a combination of molecular sieve andadsorbed perhalogenated uid that Iwould `desor-b the perhalogenatedliuid at the temperature at which the apparatus is normally operated, sothat the perhalogenated iiuid will `be able to ll such void spaces,thereby increasing their dielectric strength and overcoming the defectin the apparatus which Iwould be present .if the void were filled withair or if the void were a vacuum. In the absence of voids, the sol-idresinous material surrounding the molecular sieve acts as a closedcontainer retaining the adsorbed perhalogenated uid on the molecularsieve. `On the other hand, if the application for the composition is formaking arc extinguishing devices, then one would want to choose acombination of molecular sieve and adsorbed perhalogenated Huid whichwoul-d not -desorb any of the perhalogenated fluid at the normaloperating temperature of the equipment but only during those times whenan arc is lformed in the apparatus so that only the heat of the arccauses desorption of the perhalogenated fluid from the molecular sieve.

Likewise, if the molecular sieve containing the adsorbed perhalogenatedfluid is to be incorporated into the organic resinous material, bycompounding on a set of differential rolls, whereby the composition isnot under pressure, then one must choose a combination of molecularsieve and perhalogenated uid which does not desorb the perhalogenatedfluid at the temperature of mixing the molecular sieve containing theadsorbed perhalogenated fluid Withe the organic resinous material.However, if the compounding is carried out in a pressure apparatus whichpermits the pressurized atmosphere of the perhalogenated fluid to bemaintained over the composition While it i-s being compounded, it ispossible to compound Y `the composition without causing desorption ofthe perhalogenated duid `from the molecular sieve. Another `alternativemethod can be used whereby the molecular sieve is rst compounded withthe organic resinous material and there-after subjected to a pressurizedatmosphere of the perhalogenated fluid lfor a time suicient to cause theperhalogenated fluid to be adsorbed on the molecular sieve dispersed inthe organic resinous material. Various alternatives can be used todecrease the time required to saturate the molecular sieve such as forexample by having the organic resinous material containing the molecularsieve in extremely finely divided form, by heating, etc. If the organicresinous material is a thermoplastic resin, it is preferable to heat thecompounded thermoplastic resin and the Imolecular sieve to a temperatureWhere the thermoplastic resin is soft and then cooling the compositionwhile maintaining the pressurized atmosphere of therperhalogenated fluiduntil the composition is cooled below the temperature at which theperhalogenated fluid is desorbed from the molecular sieve.

Whether a particular perhalogenated fluid will be adsorbed and at whattemperature it will be rapidly desorbed from a particular molecularsieve may be readily determined by consideration of the pore size of themolecular sieve and the critical dimension of the molecule of theperhalogenated fluid, and the readily determined adsorption anddesorption isotherm of the particular perhalogenated fluid on theparticular molecular sieve.

If the compounding of the molecular sieve with the organic resinousmaterials is to be done with a liquid organic resinous material such asIa casting resin, for example a liquid phenolic resin, a liquid epoxyresin or a liquid polyester resin, for example one of the solventlessvarnishes, or a polymerizable monomer, then compounding can take placeat room temperature and there is no problem involved in the mixing ofthe molecular sieve already having the perhalogenated uid adsorbed onit.

Once the mixture of the organic synthetic resin and the molecular sievehaving the perhalogenated fluid adsorbed on it has been made, the actualfabrication of the insulation for the electrical apparatus can bereadily carried out using the conventional techniques. For example, thecompound can be extruded onto an electrical conductor, molded into theplates for -an arc chute, or for the fuse or arc chamber, or can be usedas `a molding compound to encapsulate electrical apparatus such as atransformer. Since these fabrication techniques are carried out underpressure and the objects can be cooled under pressure, no desorption ofthe perhalogenated iluidA occurs during the molding operation. :If aliquid resin such as those mentioned above is used to encapsulateelectrical apparatus, the Iactual curing of the liquid org-anic resinousmaterial with heat can be carried out using a pressurized atmosphere ofthe perhalogenated liuid above the liquid which is maintained until thepolymer has been cured to the solid state and cooled below thetemperature where desorption of the perhalogenated fluid would occurfrom the molecular sieve. lf the insulation is to be in the form of arolled tube of a fabric such as paper or cloth, by rolling the sheet offabric around a removable mandrel and impregnating the paper by meltingof the resin as the rolling operation takes place, then it isV necessaryto use a combination of molecular sieve and perhalogenated fluid whichdoes not desorb at the temperature at which the tube is rolled. However,this is the type of combination that would be desirable for such afabrication technique, since t'he use of such tubes is for arc chambers,fuse tubes, etc., where it is desired to have the 'generation of gasoccur under the influence of an electrical arc.

In order that those skilled in the art may better understand how thepresent invention may be practiced, the following examples are given byway of illustration and not by way of limitation.

Example 1 The molecular sieve designated as 5A, is made by replacing 75percent of the sodium ions with calcium ions of the molecular sievedesignated as 4A, having the chemical composition:

0.96 i 0.04Na2O.Al2O3.1.92 i 0.09SiO2-XH2O where X represents the numberof molecules of Water associated with the crystal structure which isremoved prior to adsorption. VIn the fully hydrated form X is 27. Thestructure is cubic, a: 12.32 A., space group Ol/h Pm3m. This molecularsieve was outgassed to remove the water of hydration at 350 C. for 15hours and allowed to cool in vacuum, after which an atmosphere of 2,000millimeters pressure was obtained by admitting dichlorodifluoromethaneat room temperature and allowing the adsorption of thedichlorodiuoromethane on the molecular sieve to come to equilibrium overa period of 7 days. A total of 0.193 gram of the dichlorodiuoromethaneper gram of molecular sieve was adsorbed. This perhalogenated fluid wasso tightly held by the molecular sieve that when this combination wassubmitted to a vacuum of 0.01 micron, no desorption of thedichlorodifluoromethane occurred. Likewise, when a sample of thismolecular sieve was heated no desorption of the gas occurred until atemperature of 290 C. was reached,

after which gas begins to desorb and becomes rapid at approximately 310C.

Dichlorodiuorornethane has a molecular size, expressed in angstroms, ofa width of 4.93, a depth of 4.90 and a length of 6.64. Since themolecular sieve used is generally designated as having a uniform poresize of angstroms, the critical dimension of this molecule is its width,which is just slightly smaller than the pore size of the molecularsieve. The use of high pressure has therefore forced these molecules ofdichlorodifluoromethane into the pores of the molecular sieve, in muchvthe same way as one forces a cork into a bottle where the molecules arenow tightly held as shown by the high temperatures required to causedesorption of these molecules. The critical dimensions of some of theother perhalogenated alkanes also have approximately the same criticaldimension and therefore are also tightly held on this molecular sieve.

This combination of molecular sieve and perhalogenated fluid is ideallysuited for compounding into molding compositions which do not requireprocessing temperatures exceeding 290 C., since no desorption will occurduring such processing steps. Such a combination therefore is admirablysuited for incorporation into such organic resinous materials asphenolic resins, urea resins, melamine resins, and all of thethermoplastic types of resins, all of which can be compounded attemperatures under 290 C., with this combination of molecular sieve andperhalogenated fluid, to yield molding compositions, or impregnatingcompositions, which can be fabricated into insulating components ofelectrical apparatus by usual molding or impregnating techniques. Thiscombination of molecular sieve and adsorbed perhalogenated Huid can alsobe mixed with solutions of the above type resins or with liquid orsemi-solid casting resins, for example, polymerizable monomers, liquidphenolic resins, epoxy resins, polyester resins including the so-calledsolventless varnishes, etc., even at room temperature, to disperse themolecular sieve with its adsorbed perhalogenated fluid in the resinousmaterial. Such filled compositions can be used to impregnate varioustypes of fibrous or fabric materials, for example, paper cloth, mattedor woven glass fibers, which can be molded into laminated sheets, woundinto tubes, rods, etc., or molded to a desired shape. The liquid fillercontaining compositions can also be cast into any desired shape or usedto encapsulate or encase a desired piece of electrical apparatus toprovide insulation therefor. Such liquid compositions are readilypolymerized or cured to the solid state by use of heat, catalysts, etc.,at temperatures well under 290 C., so that no precautions have to betaken to prevent desorption of the perhalogenated uid from the molecularsieve dispersed in the resin. All such fabricated parts make ideal arcextinguishing devices which will rapidly desorb the perhalogenated iluidwhen exposed to the heat of an electrical arc.

Example 2 A molecular sieve designated as 13X has the chemicalcomposition:

and has the cubic structure, (1:24.95 A., space group O7/ hFd3m. It isregarded as having a uniform pore size of 13 angstroms. Sulfurhexafiuoride has a spherical shape and has a critical diameter of 5.8angstroms. It can be readily adsorbed on the molecular sieve 13X afterit has been dehydrated, to remove the water. A sample of molecular sieve13X was dried in vacuo for several days at 300-40-0 C. to remove thewater. A molding powder was prepared from this molecular sieve by mixingit with polymethylmethacrylate powder in the ratio of 40% by weight ofthe molecular sieve and 60% by weight of the polymethyl-methacrylate, bygrinding the two components together in a ball mill for 16 hours.

Sheets were then molded of this material in a compression type mold at200 C., using a ram pressure of 1,000 p.s.i.g., to give sheets 3 x 4inches x /16 inch thick. A portion of these molded sheets was used toprepare a test blank and the balance of the material was cut into smallstrips and placed in a glass-lined pressure vessel and heated for 88hours at 170 C. under pressure of 750 p.s.i.g. of sulfur hexaiiuoride.At the end of this time, the pressure vessel was cooled to roomtemperature. The strips were removed and molded into sheets using acompression type mold at 170 C. and 1500 p.s.i.g. pressure, and cooledto room temperature while maintaining pressure on the molded part.Analysis of a sample of this molded material showed that it contained0.94% by weight of sulfur hexaiiuoride. In another impregnation run, asample was heated for 168 hours at 190 C. using a pressure of 300p.s.i.g. of sulfur hexauoride. This sample was molded at a temperatureof 200 C. using a ram pressure of 700 p.s.i.g. and cooling to roomtemperature before removing the pressure. Analysis of this molded partshowed that it contained 1.3% by weight sulfur hexaliuoride. The blankand the two materials containing the adsorbed sulfur hexaiiuoride on themolecular sieve were fabricated into arc chute components 1% inches widex 2 inches high, having a triangular notch 1 inch wide x l inch high inthe lower edge. Four of each of such segments spaced 1A; inch apart wereassembled as illustrated in FIG. 4 such that the V-notch of each piecewas made to straddle the arcing electrodes which were two 1% inchcylindrical copper electrodes with a normal gap of -/s inch when open. Ahigh voltage pulse from a 60-cycle power source was used and oninterruption by opening of the electrodes, an electric arc formed whichwas magnetically deflected over the surface of the arc chute segments.The average arc recovery strength of the gap between the open electrodeswas determined for currents of both 400 and 1400 amperes. For 60- cycleoperation, the arc recovery strength in about 2 milliseconds isimportant. Both of the samples containing the 0.94 and 1.3% adsorbedsulfur hexailuoride had a higher arc recovery strength than the arcchute material prepared from the polymethylmethacrylate containing onlythe molecular sieve with no adsorbed sulfur hexafluoride when measured 2milliseconds after opening of the electrodes.

Example 3 A molecular sieve designated 13X and described in Example 2was milled on a set of differential rolls with polyethylene to give amolding composition containing 40% by weight of the molecular sieve.This composition was molded into 25- and 40-mil thi-ck sheets. Part ofthis material was cut into 1inch strips and placed in la pressure vesselheated to 150 C. under a pressure of 570 p.s.i.g. of sulfur hexauoridefor 27 hours and then cooled to room temperature while maintaining thepressure. The material was pressed into 25- and 40-mil sheets bypressing `at C. under a pressure of about 2000 p.s.i.g. Analysis of thismaterial showed that it contained 8.9% by weight of adsorbed sulfurhexaifluoride. To test the ability of this composition to fill a voidwith sulfur hexafluoride and raise the corona starting voltage, thecomposition containing only the molecular sieve and the compositioncontaining the molecular sieve with the adsorbed sulfur hexaiiuoridewere each made into a test part having a standard void. The test partswere made by placing -a 2-inch diameter x 25 mil circular disc with a%-inch hole in the center between two 2-inoh diameter X 40-mil discs andthen heat-sealing the edges of the three discs, to provide a centralvoid inch X 25 mils in each of the test parts. One-inch diameterelectrodes were painted on the upper and lower faces of each of tihesamples with a silver paint. A 60-cycle voltage was then applied to theelectrodes with the voltage being increased until corona.

pulses were detected in a standard test circuit at room temperature.

The test part having no sulfur hexafluoride adsorbed on the molecularsieve had an average corona starting voltage of 1.8'8 KVRMS (kilovolts,root mean square), whereas the test piece containing the adsorbed sulfurhexauoride had an average corona starting voltage of 2.50 KVRMS,immediately after fabrication of the test parts. After heating at 37 C.for 15 hours, the corona startin-g voltage for the sample containing nosulfur hexafluoride was still the same, whereas the sample containingthe sulfur hexafluoride had risen to 3.16 KVRMS. The test pieces werethen placed in an oven at 105.5 C. for 5.25 hours and re-measured, butagain the sample containing no sulfur hexaflu-oride showed no change incorona starting voltage, whereas the sample containing sulfurhexatluoride had increased to an average of 6.31 KVRMS. After standingan additional 2 weeks at room temperature, the test part containing nosulfur hexafluoride still had the same corona starting voltage, whereasthe sample containing the sulfur hexafluoride had an average coronastarting voltage of 5.28 KVRMS.

When the molecular sieve of this example was loaded with sulfurhexafluoride prior to compounding with the polyethylene, and thenfabricated as described above, it was found that the compound onlycontained 1.2% sulfur hexauoride, showing that for this combination ofmolecular sieve and perhalogenated fluid, a higher content of adsorbedperhalogenated fluid could be obtained by adsorbing the perhalogenatedfluid after, rather than prior to, the formation of the moldingcompound, but that either method could be used to obtain a compositioncontaining adsorbed perhalogenated fluid.

Example 4 A molecular sieve designated as 5A described in Example 1 wasdried for 24 hours at 360 C. under vacuum. After cooling to roomtemperature, the vacuum was broken by admitting dichlorodifuoromethaneto give a pressure of 760 millimeters. As the gas was adsorbed on themolecular sieve, the pressure slowly decreased, additionaldichlorodifluoromethane was admitted to raise the pressure to 760millimeters several times until the pressure remained constant at 760millimeters, all pressures being in terms of millimeters of mercury.Analysis of the molecular sieve showed that a total of 9.6% by weight ofdichlorodiiluoromethane had been adsorbed.

A mixture of 40% by weight of the above molecular sieve containing theadsorbed dichlorodifluoromethane and 60% by weight of powdered.polymethylmethacrylate were ball-milled together for 24 hours to give auniform dispersion of the two ingredients. This mixture was molded at178 C. in a flash-type mold for 2 minutes and cooled to room temperatureto form sheets 6 x -6 inches square x 60 mils thick. Analysis of themolded parts showed that they contained 4.27% by weight of thedichlorodiuoromethane. Correcting for the methyl methacrylate componentof the sample, this value shows, within the experimental accuracy of theanalysis, that during the ball-milling and molding operation none of thediohlorodiuoromethane had been desorbed from the molecular sieve. Such amolding compositionY is suitable, therefore, for the production ofmolded parts Where release of the dielectric fluid is desired attemperatures higher than those used in the production of the moldedparts.

While several embodiments have been illustrated in the above examples,it will be apparent to those skilled in the art that variousmodifications are contemplated to be within the scope of this invention.-For example, other fillers, dyes, pigments, plasticizers, stabilizers,etc., may be incorporated in the compositions. Therefore, the appendedclaims are intended to cover all such equivalent variations as comewithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A fabricated electrical insulating body comprising an organicresinous material having dispersed therein a molecular sieve havingadsorbed thereon a perhalogenated fluid having a dielectric strengthgreater than air, said body being free of porosity caused by desorptionof said uid from the molecular sieve.

2. The composition of claim 1 wherein the perhalogenated fluid is sulfurhexatluoride.

3. The composition of claim 1 wherein the perhalogenated uid is aperhalogenated alkane.

4. In an electrical device having spaced elements adapted to have anelectrical potential developed therebetween, an insulating memberinterposed lbetween said spaced elements comprising an organic resinousmaterial having dispersed therein a molecular sieve having adsorbedthereon a perhalogenated fluid having a dielectric strength greater thanair, said insulating member being free of porosity caused by desorptionof Said fluid from the molecular sieve.

5. In an electric arc extinguishing apparatus having spaced elementsadapted to have an electrical arc established between the spacedelements, an arc extinguishing element whose surface is contacted bysaid arc, said arc extinguishing element being formed of a compositioncomprising an organic resinous material having dispersed therein amolecular sieve having absorbed thereon a perhalogenated fluid having adielectric strength greater than air, said arc extinguishing element1being free of porosity caused by desorption of said uid from themolecular sieve.

6. An electrical conductor in contact with insulation comprising anorganic resinous material having dispersed therein a molecular sievehaving adsorbed thereon a perhalogenated uid having a dielectricstrength greater thank air, said insulation being free of porositycaused by desorption of said fluid from the molecular sieve.

7. The process of producing an electrical insulating member whichcomprises shaping under heat and pressure a composition comprising anorganic resinous material having dispersed therein a molecular sievehaving adsorbed thereon a perhalogenated fluid having a dielectricstrength greater than air, and cooling the shaped composition whilemaintaining suicient press-ure on the shaped composition that the uidadsorbed on the molecular sieve is prevented from expanding and therebycausing porosity of the shaped composition.

8. The process of producing a moldable organic resin-ous materialcontaining a molecular sieve having adsorbed thereon a perhalogenatedfluid having a dielectric strength greater than air which comprisesblending said organic resinous material with said molecular sieve havingadsorbed thereon said perhalogenated uid, said blending lbeing carriedout at a temperature where said resinous material will fuse and coat themolecular sieve but below the temperature which will cause theperhalogenated fluid to be desorbed from the molecular sieve.

9. The process of claim 8 wherein the perhalogenated tiuid is sulfurhexafluoride.

10. The process of claim 8 wherein the' perhalogenated uid is aperhalogenated alkane.

11. The method of making moldable thermoplastic organic resinousmaterial containing a molecular sieve having adsorbed thereon aperhalogenated fluid having a dielectric strength greater than air whichcomprises (l) heating said resinous material containing the molecularsieve dispersed therein to a temperature where said resinous material isuid in a pressure vessel, (2) pressurizing said vessel with saidperhalogenated -lluid while maintaining said resinous material in theuid state, and (3) maintaining the pressure while cooling said resinousmaterial to a temperature below that which would cause saidperhalogenated fluid to be desorbed from said molecular sieve.

13 14 12. The process of claim 11 wherein the perhalogenated OTHERREFERENCES Huid is sulfur hexafluoride. h l h b1 13. The proces of claim11 wherein the perhalogenated C013; rslgcl' snnclldlg Sltves Rem 01d PuIshmg fluid is a perhalogenated alkane.

5 References Cited by the Examiner ROBERT K. SCHAEFER, Puma/y Exammel.

UNITED STATES PATENTS K. H. CLAFFY, ROBERT S. MACON, P. E. CRAW- FORD,Assstant Examiners. 2,912,382 11/1959 Liao et al. 252-63.2

1. A FABRICATED ELECTRICAL INSULATING BODY COMPRISING AN ORGANICRESINOUS MATERIAL HAVING DISPERSED THEREIN A MOLECULAR SIEVE HAVINGABSORBED THEREON A PERHALOGENATED FLUID HAVING A DIELECTRIC STRENGTHGREATER THAN AIR, SAID BODY BEING FREE OF POROSITY CAUSED BY DESORPTIONOF SAID FLUID FROM THE MOLECULR SIEVE.